1. Field of the Invention
The present invention relates generally to a tape cassette for use in recording a digital signal, such as, a PCM (pulse code modulated) signal and the like. More particularly, this invention relates to a tape cassette in which a spring for biasing a brake member to restrict the rotation of a reel hub can be positively prevented from being positionally displaced.
2. Description of the Prior Art
There has been proposed a PCM (pulse code modulated) signal recording and reproducing apparatus in which an analog signal such as an audio signal or the like is converted to a digital signal, for example a PCM signal, and then recorded on (or reproduced from) a magnetic tape. The known PCM recording and reproducing apparatus utilizes a rotary magnetic head so as to provide a relatively high recording density. According to such PCM recording and reproducing apparatus utilizing the rotary magnetic head, upon recording and/or reproducing, a magnetic tape is drawn out of a tape cassette, loaded on a rotary drum on which the rotary magnetic head is mounted, and then the recording and/or reproducing is carried out.
It has been found that in the case of a magnetic tape, if a user touches the magnetic tape with his fingers and smudges the tape with an oily component or dust, a dropout will occur in the reproduced signal. Accordingly, it is important that the magnetic tape incorporated in the tape cassette be sealed as tightly as possible so as to protect the tape from being touched by the user with his fingers or being open to dust and the like.
As a prior art tape cassette of this kind, there is one previously proposed by the assignee of the present application as, for example, Japanese Utility Model application No. 60-156119.
This previously proposed tape cassette will be described with reference to FIGS. 1 to 3.
In the figures, reference numeral 1 designates a cassette housing. The cassette housing 1 is formed of a pair of an upper half 2 and a lower half 3 that are screwed together. A transparent window plate 2a is formed on an upper surface portion of the upper half 2. A pair of reel hubs 4a and 4b are incorporated within the cassette housing 1, and are rotatably inserted through a pair of reel shaft insertion openings 5a and 5b formed through the lower half 3 at its predetermined positions. A magnetic tape 6 is carried by, and wound around, the pair of reel hubs 4a and 4b.
Tape guide posts 7a and 7b are provided near the left and right side wall portions of the lower half 3 in opposing relation to the front portion of the cassette housing 1. The magnetic tape 6 is wound around the tape guide posts 7a and 7b so as to freely travel relative to the front portion of the cassette housing 1 at its predetermined design position. A substantially rectangular-shaped cut-away portion 3a is formed through the lower half 3 over a predetermined width, behind the magnetic tape 6 wound around the tape guide posts 7a and 7b. The cut-away portion 3a and the inside of the cassette housing 1 are shielded by a front wall 2b of the upper half 2 and a front wall 3b of the lower half 3. Upon recording or reproducing, a guide system for drawing the magnetic tape 6 is inserted into the cut-away portion 3a from the recording and reproducing apparatus, not shown.
A front lid 8 is pivotally supported at the front side of the cassette housing 1 by arm portions 8a and 8b such that the front lid 8 is able to open and close the front portion of the cassette housing 1.
A slider or sliding member 9 of substantially C-shaped cross section is slidable back and forth in opposing relation to in the lower surface portion and the left and right side walls of the lower half 3. Reel shaft insertion corresponding openings 9a and 9b are formed through the sliding member 9 to correspond to the reel shaft insertion openings 5a and 5b when the sliding mmber is slid backward so as to expose the cut-away portion 3a.
When the sliding member 9 is slid forward, and the state that the front lid 8 is closed, the reel shaft insertion corresponding openings 9a and 9b are arranged so as not to correspond to the reel shaft insertion openings 5a and 5b of the cassette housing 1 and the cut-away portion 3a of the cassette housing 1 is closed with the result that the inside of the cassette housing 1 is tightly, substantially completely, sealed. Thus, the magnetic tape 6 is protected from being smudged and is prevented from being touched by the fingers of a user.
In this condition, side plate portions 9c and 9d of the sliding member 9 are placed below the arm portions 8a and 8b of the front lid 8, the upper end edges of the side wall portions 9c and 9d of the sliding member 9 abut against the lower end edges of the arm portions 8a and 8b of the front lid 8 to thereby lock the front lid 8 so as to prevent its pivoting, the front lid 8 being thereby prevented from being opened unintentionally.
In order to prevent that in this non-use state, the tape reels 4a and 4b housed in the tightly-sealed cassette housing 1 are rotated unintenionally, and hence the magnetic tape 6 is slackened, due to vibration, shock or the like, a reel brake member 11 is provided within the cassette housing 1.
The brake member 11, of substantially U-shaped cross section, is formed of an upper support plate portion 11a extended along the rear surface of the upper half 2, and leg portions 11b and 11c which extend downwardly from the left and right end portions of the upper support plate portion 11a. At the rear end edge of the upper support plate portion 11a, brake projection members 11d and 11e project into association with ratchet wheel portions 4c and 4d formed around the respective reel hubs 4a and 4b. Operation portions 11g and 11h are formed on the end portions of the leg portions 11b and 11c of the upper support plate portion 11a.
To projecting pin 13 formed at the central portion of the upper support plate portion 11a of this brake member 11, there is attached a spring 14 which extends so as to become V-shaped as it approaches its both end portions. The curbed end portions of this spring 14 are closely contacted with and engaged with the rear surface of the front wall 2b of the upper half 2.
Left and right elongated openings 15 are formed through the upper support plate portion 11a of this brake member 11. This brake member 11 is attached through the elongated openings 15 to pins 16 that project downward from the rear surface of the upper half 2 such that the brake member 11 is slidable back and forth relative to the pins 16.
When the tape cassette is stored, or the tape cassette is not in use, this brake member 11 is slid backwards by the spring or biasing force of the spring 14 and the brake projections 11d and 11e are engaged with the ratchet wheels 4c and 4d of the reel hubs 4a and 4b to thereby lock the reel hubs 4a and 4b against rotation. Futher, when the brake member 11 is located within the cassette housing 1, end portions 11g and 11h of the operation portions are projected through operation portion insertion openings 12a, 12b of the lower half 3 to the outside of the side wall front end portions thereof by a predetermined amount. Accordingly, when the front lid 8 is pivoted upwards, the projecting portions 11g and 11h are contacted by the end portions of the arm portions 8a and 8b of the front lid 8, and the brake member 11 is slid forward against the spring or biasing force of the spring 14 so that the brake projections 11d and 11e are disengaged from the ratchet wheels 4c and 4d of the reel hubs 4a and 4b, permitting the reel hubs 4a and 4b to become rotatable.
In such prior art tape cassettes, however, since the end portions of the spring 14 of the brake member 11 only make contact with the rear surface of the front wall 2b of the upper half 2, it may occur, due to the impact when the tape cassette is assembled or when it is dropped, that the end portions of the spring 14 on the front wall 2b and become displaced downwards. Then the spring 14 cannot give the necessary positive biasing force to the brake member 11 and the spring 14 may interfere with the magnetic tape 6, etc.